We have previously identified and characterized a cDNA coding for neural membrane protein 35 (NMP35). We showed that NMP35 mRNA is predominantly expressed in the adult CNS with a neuronal expression pattern. Functional analysis indicates that the human homologue of NMP35, Lifeguard, plays a role in Fas-mediated cell death. In this study we used affinity-purified antibodies raised against the putative cytoplasmic N-terminal domain of NMP35 to determine its precise subcellular localization in the adult CNS. NMP35 protein is widely expressed throughout the brain and spinal cord, most prominently in dendrites of several neuronal cell types and in the surrounding neuropil. Immunofluorescence confocal microscopy reveals colocalization of NMP35 with the glutamate receptor GluR2 and adjacent localization to the presynaptic vesicle protein synaptophysin. These data suggest that NMP35 may be localized to the postsynaptic membrane. Immunoelectron microscopy with NMP35 antibodies confirms the expression of the protein in dendritic processes and in a subset of synapses at the postsynaptic membrane and density. These findings suggest a role for NMP35 in synapses of the adult central nervous system.